Handheld or otherwise portable analyzer devices are frequently used in the field e.g. for recognizing and sorting objects according to material(s) they contain. As a few examples, a portable analyzer device may be used in places like scrapyards, dumping grounds and recycling centers, while they also have more generic commercial and industrial use.
While several techniques for analyzing a sample under study are available for in analyzer devices of such type, optical emission spectroscopy is widely employed in portable analyzer devices to determine elemental composition of the sample under study. Herein, such analyzer devices are referred to as optical analyzers. An optical analyzer typically includes an excitation assembly for invoking an optical emission from a surface of a sample under study, a detector assembly for capturing signals that are descriptive of the optical emission so invoked, and an analysis means for determining elemental composition of the sample under study on the basis of the captured signals.
Laser-induced breakdown spectroscopy (LIBS) is widely used technique for optical emission spectroscopy, and an analyzer device making use of LIBS may be referred to as a LIBS analyzer. In a LIBS analyzer, the excitation means comprises a laser source that is arranged to generate a high peak power laser pulse. The laser pulse is focused to the sample under study to form a plasma plume on a surface of the sample in order to cause atomization and excitation on the surface. This causes light emission at wavelength(s) that are characteristic to elements on the surface of the sample. The signal descriptive of the light emission from the sample are captured at the detector means, which then passes the captured signals for the analysis means for determination of the elemental composition of the sample. Since all elements emit light that exhibit wavelength(s) characteristic thereto in response to such excitation, the relative intensities of different wavelengths indicated in the captured signals reveal the elemental constitution of the sample.
Another example of optical emission spectroscopy is Raman spectroscopy that includes a laser source as the excitation means to invoke electromagnetic radiation from the sample, which electromagnetic radiation is captured by the detector means. A further example of optical emission spectroscopy is near infrared (NIR) spectroscopy, which is a special case of Raman spectroscopy where the excitation means includes a NIR laser.
In the framework of optical emission spectroscopy that relies on a laser as the excitation means, the laser beam needs to be focused on the surface of the sample in order to effectively invoke the optical emission from the sample. Moreover, in order to ensure reliable analysis due to small variations in composition of the sample on its surface, during an analysis cycle the laser beam is moved to cover an area of the sample surface instead of focusing the laser beam in a single spot on the surface of the sample. This ensures that possible small variations in composition of the sample are ‘averaged’ over the area, thereby resulting in a more reliable analysis result.
In known solutions, the laser beam is moved along the surface of the sample during an analysis cycle by moving an optical component (e.g. a mirror or a focusing lens) via which the laser beam is guided on the surface of sample or by tilting a laser assembly about a pivot axis. However, moving the optical component or tilting the laser assembly about the pivot axis creates an arc-like movement of the laser beam with respect to the sample surface and hence results in changing the distance between the laser source and the surface of the sample. Consequently, the laser beam is not correctly focused on the surface of the sample over the whole analysis cycle. This typically leads into inefficient production of optical emission from the surface of the sample (e.g. in case of LIBS out-of-focus laser beam results in inefficient plasma formation on the surface of the sample), which in turn is likely to result in reduced accuracy and/or reliability of the analysis.